Radio-frequency transmission line section



June 27, 1950 H. E. KALLMANN 2,512,945

RADIO FREQUENCY TRANSMISSION LINE SECTION Filed June 28, 1946 2 Shee'ts-Sheet 1 2 TTTTT IN VEN TOR.

r E Kwanza- June 27, 1950 H. E. KALLMANN 2,512,945

RADIO FREQUENCY TRANSMISSION LINE SECTION Filed June 2a. 1946 2 Sheets-Sheet 2 a;/1/m/lfilllmlqmmlnnMum/n0/10 4i Patented June 27, 1950 UNITED s'rpi'rrs PATENT OFFICE RADIO-FREQUENCY TRANSMISSION LINE SECTION Heinz E. Kallmann, New York, N. Y. Application June 28, 1946, Serial No. 679,920

My present invention relates to circuit elements for very high radio frequencies, particularly for that region of wavelengths where the reactances of lumped resonance circuits are no longer large compared with incidental ones such as of the wiring and tube electrodes.

t is usual to replace tuned resonance circuits for these frequencies by sections of twin conductor lines, be they parallel wires as first suggested. by Lecher, or sections of. coaxialcables. A particularly important line section is that whose electrical length equals one-quarter wavelength. This quarter wave line section is, for example, used for matching lines of diiferent impedances. and, if its far end is short-circuited, as a circuit element of very high input impedance at a certain frequency, then taking the place of the par allel resonance circuit used at lower frequencies.

It is not inconvenient to build. the quarter Wave line section as an actual line for such high frequencies where a. quarter wave length is of the order of a few inches or less, that is, at and above frequencies of 1,000 megacycles. However, as explained above, it is desirable to use line sections already at much lower frequencies such as in the range between 20 and 1,000 megacycles, where a quarter wave line section may be as long as 12 feet. Even if the line section is built of a cable with dielectric of the dielectric constant 7c=2.25, the physical length of the quarter wave line section reduces only by /F=.6'Z relative to its electrical length.

In order to overcome the. above discussed difficulties, it is an object of my present invention to provide condensed line sections that are in a small space equivalent to relatively long sections of lines.

It is a further object of my present invention to provide line sections thatv may be made of any desired matching impedance including such values as are quite impracticable with usual lines.

It is also an object of my invention to provide sections, particularly quarter wave line sections, which have in spite of small volume a very high equivalent Q factor and which maintain their electrical length unchanged in the course of time.

15 Claims. (Cl. 17844) Furthermore, it is an object of my invention to I provide line. sections with any desired, or zero, temperature coefficient of electrical length.

Still another object of my invention is to construct line sections which are so small in size that they can be mounted on moving parts of I fine adjustment of their electrical length without cutting or piecing. 7

Finally, it is also an object of my present invention to provide a line section whose inductance and capacitance, while still substantially distributed, are concentrated into a small space, so that, for example, the advantages of quarter wave line sections can be had with a tuning element that is perhaps 20 times: shorter than a conventi-onal quarter wave line section.

With the above objects in View, my new shorted line section mainly consists of a coiled forward conductor, and a return conductor electrically connected at its one end to one end of this coiled forward conductor and arranged at a slight distance from the same so as to create a substantially distributed capacitance between the two conductors.

In order to connect the shorted line section to other electrical elements, it is advisable to provide contact members at. the free unconnected ends of the conductors forming part of the: sec tion.

As mentioned above, the return conductor has to be dimensioned and placed so as to create a substantially distributed capacitance between the two conductors. I have found that this object can be best achieved if the returncond'uctor is arranged closely spaced from the coiled forward conductor crossing at least at several points the path of the same.

The return conductor mentioned above might be either straight or coiled. If it is coiled,- it should becoiled in reverse direction to the coiled forward conductor as will be described farther below in detail.

In order further to increase the capacity between the conductors, I place between the two conductors described above an insulating member consisting of a material with a high dielectric constant, preferably a ceramic body.. A line section of this type consists of a ceramic tube as the insulating member, a coiled forward conductor arranged on one face of this insulating member in close contact with the same, and a return conductor arranged on'the other face of the insulat ing'member in close contact with the same and connected at its one: end to one end of the. coiled forward conductor mentioned above.

In the-eventthat. an insulating. ceramic tube is used, the coiled forward conductor is arranged either' on the outer or the inner surface of the tube and the return conductor arranged on the other surface; both conductors are connected to each other at one end of: the tube.

I have found that linev sections of the above described type are substantially shorter than correspondinglinesections of conventional construction. The theoretical considerations on which this fact is based are the following:

The electrical length Z, in centimeters, of the line section is Z: T22 where T is the time required for an electrical wave to travel its length and I where v in centimeters per second is the velocity The of propagation, that is, 3.10 in free space. value of T can be found for any network from the equation T=\/LC', where L in henries and C in farads are the values of the total series inductance and of the total shunt capacitance of the network. Thus, Z=3.10 VE; it may be in-g creased for any line by increasing the distributed series inductance or the distributed shunt ca-" pacitance of the line, or both. The former is done;

by coiling one or both conductors, the latter by their close spacing and by insertion of material with a' high dielectric constant between them. The matching impedance Z= /L/C does not dimethod of operation, together with additional ob- I 30 jects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings; in which:

Fig. 1 is a semi-schematic view of a shorted line section according to my-present invention;

Fig. 2 is a perspective view of an embodiment of a line sectionaccording to my present invention; I

Fig. 3'is a top view of the line section shown in Fig. '2, cut open in axial direction and bent apart; Fig. 4 .is a top viewsimilar to the one shown in Fig. 3 of a modified line section;

Fig. 5 is a top view similar to the one shown in Fig. 3 of another modified line section;

Fig. 6 is a longitudinal section throu h. still another shorted line section according to my present invention; I

Fig. 7 is a side view of a further'embodiment of a line sectionaccording to my present invenr tion; I

Fig. 8 is a longitudinal section through the line section shown in Fig. 7; 1 V v i Fig.9 is a top view of a disc-shaped line section according to my present invention; Fig. 10'is a side view of the linesection shown in Fig. "9, seen in direction "of 1 arrow 'Illof Fig. ggandly I I. v

Figi 11 is a longitudinal section through a line section of thetype shown in Figsjz and 3' pro 'vide'd with adjustingm eans.

' The semi-schematic shorted line section shown in Fig. 1 is theoretically obtained by increasing both' the distributed series inductance and" the distributed "shunt capacitance of a" parallel or coaxial line of conventional type. "In this line section, the coiled forward conductor is connected with the returnconductor 2 l as indicated at 22, thus forminga shorted line section. One

contactfmember 23 is arranged at the unconnected end of the coiledforward conductor 20 and another contact member 24 is arranged at the unconnected end of the returnc'onductor 2 l.'

In order to obtain the desired distributed'shunt capacitance, the line section shown in Fig. 1 is loaded with a series of shunt condensers 25 as shown.

A preferred form of a line section according to my present invention is shown in Figs. 2 and 3. As shown in these figures, the forward conductor 26 is coiled around an insulating tube 21 and connected at its one end as indicated by 28 to a returnconductor 29 arranged inside the insulating tube in contact with the inner surface of the same. In this way the forward conductor 26 and the return conductor 29 are closely spaced, i. e.

only at a slight distance from each other so that v the shunt capacitances between them, particularly at the points of intersection indicated in Fig. 3 by 30 are relatively high.

As mentioned above, it is Of importance that the forward conductor is coiled. However, it is not absolutely necessary that the return conductor is straight as shown in Fig. 3. It is possible to coil the return conductor too, as indicated in Fig. 4 by numeral 3!, or to shapeit as indicated in Fig. 5 by numeral 32.

I wish to stress that coiling of the return constrip is added to the return conductor in order to increase the width of the conductor and thus to increase the shunt'capacity of the section. I wish tostress, however, that it is also possible to provide more, e. g. three or four, parallel returnstrips serving as return conductors and to join the same electrically at at least one point as. indicated by numeral 34 in Fig. 5.

It isalso possible, in order to further increase the shunt capacity, to substitute for the single return conductor 29 shown in Figs. 2, 3 and 4 or the two return conductors 32 shown in Fig. 5, a return conductor 35 covering the entire inner surface of the heavy walled ceramic tube 3S as shown in Fig. 6.. One end of this return conductor 35 is electrically connected by connection 31 to the coiled forward conductor 38.

I have found that I might go even further and substitute for the cylindrical return conductor 35 used in the line section shown in Fig. 6 a rodshaped return conductor 39 firmly embedded in the ceramic core 40 and electrically connected at M to the coiled forward conductor 62.

I wish to stress that the insulating member need .not be tubular as disclosed in the sections shown in Figs. 2 to 8, but I might use instead a disc-shaped insulating member 43 as shown in Figs. 9 and 10. In this event, the forward conductor 44 may have the shape of a fiat spiral and is arranged on one face, e. g. face 45 of the insulatingdisc 43 while the return conductor 46 may. be straight and is arranged on the opposite face d'l of disc 43. The two conductors are electrically connected to each otherthrough a hole 48 provided at the center of disc 43, as shown.

It iswell known that the electrical length of a line with a dielectric whose dielectric constant does not varywith temperature is simply proportional to its physical length and rises linearly with itslinear expansion coefficient. This is true for parallel and coaxial lines and would also be true for line sections of the type proposed by me if I choose an insulating member whose dielectric constant does not vary with temperature.

I haye found, however, that. I might. reduce somewhat the temperature coefficient ofthe electrical length of a line section of the. type proposed by me.. Thus, if it is desired to make a line section: with a lower temperature coeflicient e. g. the ceramic insulating tube, defines the I expansion coefiicient of the line. In this way it is possible toreduce the change of length due: to temperature changes to about half, since. metals, such as copper and silver expand about 1.'7.1O- per degree C, while a ceramic, such as stea-itite, expands only about 8.10 per degree. C.

As a further improvement in the reduction or other adjustment of the temperature coefiicientof the line, I have successfully used ceramic cores which incorporate titanium dioxide or other components whose dielectric constant decreases with increasing temperature. If, for exampiethe total dielectric constant decreases as much with rising temperature, say 8 10 per degree C. as the linear dimensions of the line increase say +8 X 10 per degree C., then the electrical length.

of the line does no longer change with temperature. Moreover, since incidental re-actances in the oscillator tube and wiring generally also contribute a slight positive temperature coefficient of wavelength, I have successfully compensated for those also by making the temperature coefficient of the dielectric constant of the line core somewhat more negative, say 2{) '10 per de-- gree C.

Furthermore, I have found that it is possible to obtain fine adjustment of the inductance of a line section of the type proposed by me by providing, as shown in Fig. 11, a conductive or paramagnetic slug 49 moved by a screw 59 and the screw threaded collar 5! Within the tubular member 52 in axial direction of the same and moving it from points of weak magnetic field near the end of the coil to points of strong magnetic field nearer its center.

I wish also to stress that although I have shown only line sections in which the coiled forward conductor is arranged on the outer surface of an insulating tube, I might in some cases also arrange the coiled forward conductor on the inner tube surface and the return conductor on the outer surface.

It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of line sections differing from the types described above by being of other length than a quarter wave, or by being open at their far end, or loaded, or any combination of these features.

While I have illustrated and described the invention as embodied in quarter-wave line sections, I do not intend to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spiritof my invention.

Without further analysis, the foregoing will so fully reveal the gist of my invention that others can by applying current knowledge readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairl'y constitute essential characteristics of the generic or specific aspects of this invention, and,

therefore, such adaptations should and are intended to; be comprehended within the meaning and range of equivalence of the following claims.

What I. claim as new and desire to secure. by Letters Patent is:

1. A line section comprising in combination a rigid insulating member having two closely spaced faces; a coiled forward conductor having a mechanical rigidity which is less than that of said rigid insulating member firmly fused to one of said faces of said rigid insulating member so that during temperature variations its expansion is identical to the expansion of said rigid insulating member; and a. return conductor having a mechanical rigidity which is also less than that of said rigid insulating member and being firmly fused to the. other of said faces of said rigid insulating member so that during temperature variations its expansion is identical to the expansion of said rigid insulating member.

2:. A line section comprising in combination a rigid insulating tubular member having an inner cylindrical face and an outer cylindrical face; a coiled forward conductor having a mechanical rigidity which is less than that of said rigid insulating tubular member firmly fused to said outer cylindrical face of said rigid insulating tubular member so that during temperature variations its expansion is identical to the expansion of said rigid insulating tubular member; and a return conductor having a mechanical rigidity which is also less than that of said rigid insulating tubular member and being firmly fused to said inner cylindrical face of said rigid insulating tubular member so that during temperature variations its expansion is identical to the expansion of said rigid insulating tubular member.

3. A line section comprising in combination a rigid ceramic tube having an innerv cylindrical face and an outer cylindrical face; a coiled forward conductor having a. mechanical rigidity which is less'than that of saidrigid ceramic tube firmly fused to said outer cylindrical face of said rigid ceramic tube. so that during temperature variations its expansion is identical to the expansion of said rigid ceramic: tube; and a return conductor having a mechanical rigidity which is also less than that of said rigid ceramic tube and being firmly fused to said inner cylindrical face of said rigid ceramic tube so that during temperature variations its expansion is identical to the expansion of said rigid ceramic tube.

4. A line section comprising in combination a rigid insulating tubular member consisting of refractory material and having an inner cylindrical face and an. outer cylindrical face; a coiled forward conductor having a mechanical rigidity which is less than that of said rigid insulating tubular member firmly fused to said outer cylindrical face of said rigid insulating tubular member so that duringtemperature variations its expansion is; identical to the expansion of said rigid insulating tubular member; and a straight return conductor having a mechanical rigidity which is also less than that. of said rigid insulating tubular member and being firmly fused to said inner cylindrical face of said rigid insulating tubular member so that during temperature variations its expansion is identical to the expansion of said rigid insulating tubular member.

5. A line section comprising in combination a rigid insulating member consisting of a material the dielectric constant of which decreases with increasing temperature and having two closely spaced faces; a coiled forward conductor having a mechanical rigidity which is lessvthan that of said rigid insulating member firmly fused to one of said faces of said rigid insulating memberv so that during temperature variations its expansion is identical to the expansion of said rigid insulating member; and a return conductor having a mechanical rigidity which is also less than that of said rigid insulating member and being firmly 8 conductor of said line section and to create a substantially distributed shunt capacitance between said coatings.

9. A line section comprising in combination a rigid insulating tubular member consisting of refractory material having an outer cylindrical face and an inner cylindrical face; a coiled stripshaped metal coating having a mechanical rigidity which is less than that of said rigid insu- Y lating tubular member firmly fused to said outer cylindrical face of said rigid insulating tubular said rigid insulating tubular member firmly fused sion of said rigid insulating tubular member; and

a straight return conductor having a mechanical rigidity which is also less than that of said rigid insulating tubular member and being firmly fused to said inner cylindrical face of said rigid insulating tubular member so that during temperature variations its expansion is identical to the expansion of said rigid insulating tubular member.

7. A line section comprising in combination a self-supporting rigid insulating member having two closely spaced faces; a coiled strip-shaped metal coating having a mechanical rigidity which is less than that of said rigid insulating member firmly fused to one of said faces of said selfsupporting rigid insulating member so that during temperature variations its expansion is identical to the expansion of said self-supporting rigid insulating member and adapted to serve as forward conductor of. said line section; and a strip-shaped metal coating having a mechanical rigidity which is also less than that of said selfsupporting rigid insulating. member and being firmly fused to the other of said faces of said self-supporting rigid insulating member so that during temperature variations its expansion is identical to the expansion of said self-supporting rigid insulating member.

8. A line section comprising in combination a self-supporting rigid insulating tubular member having an outer cylindrical face and an inner cylindrical face; a coiled strip-shaped metal coat-- ing having a mechanical rigidity which is less than that of said self-supporting rigid insulating tubular member firmly fused to said outer cylindrical face of said self-supporting rigidinsulating tubular member so that during temperature variations its expansion is identical to the expansion of said self-supporting rigid insulating tubular member, said coiled strip-shaped metal coate ing extending in longitudinal direction of said self-supporting rigid insulating tubular member and adapted to serve as forward conductor of said line section; and a metal coating having a mechanical rigidity which is also less than that of said self -supp orting rigid insulating tubular member and being firmly fused to said inner face of said self-supporting rigid insulating tubular member so that during temperature variations its expansion is identical to the expansion of said self-supporting rigid insulating tubular member, said metal coating extending in longitudinal direction of said self-supporting rigid insulating tubular member and adapted to. serve asreturn member so that during temperature variations its expansion is identical to the expansion of said rigid insulating tubular member, said coiled stripshaped metal coating extending in longitudinal direction of said rigid insulating tubular member and adapted to serve as forward conductor of said line section; and a straight strip-shaped metal coating having a mechanical rigidity which is also less than that of said rigid insulating tubular member and being firmly fused to said inner face of said rigid insulating tubular member so that during temperature variations its expansion is identical to the expansion of said rigid insulating tubular member, said straight stripshaped metal coating extending in longitudinal direction of said rigid insulating tubular member and adapted to serve as return conductor of said line section and to create a substantially distributed shunt capacitance between said coatings.

10. A line section comprising in combination a ceramic tube having an outer cylindrical face and an inner cylindrical face; a coiled stripshaped metal coating having a mechanical rigidity which is less than that of said ceramic tube firmly fused to said outer cylindrical face of said ceramic tube so that during temperature variations its expansion is identical to the expansion of said ceramic tube, said coiled strip-shaped metal coating extending in longitudinal direction of said ceramic tube and adapted to serve as-forward conductor of said line section; and a metal coating having a mechanical rigidity which is also less than that !Of said ceramic tube and being firmly fused to said inner face of said ceramic tube, said metal coating extending in longitudinal direction of said ceramic tube and adapted to serve as return conductor of said line section and to create a substantially distributed shunt capacitance between said coatings.

11. A line section comprising in combination a rigid insulating tubular member consisting of a material the dielectric constant of which decreases with increasingtemperature, said rigid insulating tubular member having an outer cylindrical face and an inner cylindrical face; a coiled strip-shaped metal coating having a mechanical rigidity which is less than that of said rigid insulating tubular member firmly fused to said outer cylindrical face of said rigid insulating tubular member so that during temperature variations its expansion is identical to the expansion of said rigid insulating tubular member, said coiled strip-shaped metal coating extending in longitudinal direction of said rigid insulating tubular member and adapted to serve as forward conductor of said line section; and a straight stripshaped metal coating having a mechanical rigidity which is also less than that of said rigid insulating tubular member and being firmly fused to said inner face of said insulating tubular member so that during temperature variations its expansion is identical to the expansion of said rigid insulating tubular member, said straight-strip-shaped metal coating extending in longitudinal direction of said rigid insulating tubular member and adapted to serve as return conductor of said line section and to create a substantially distributed shunt capacitance between said coatings.

12. A line section comprising in combination a ceramic tube consisting of a ceramic material the dielectric constant of which decreases with increasing temperature, said ceramic tube having an outer cylindrical face and an inner cylindrical face; a coiled strip-shaped metal coating having a mechanical rigidity which is less than that of said ceramic tube firmly fused to said outer cylindrical face of said ceramic tube so that during temperature variations its expansion is identical to the expansion of said ceramic tube, said coiled strip-shaped metal coating extending in longitudinal direction of said ceramic tube and adapted to serve as forward conductor of said line section; and a straight strip-shaped metal coating having a mechanical rigidity which is also less than that of said ceramic tube and being firmly fused to said inner face of said ceramic tube so that during temperature variations its expansion is identical to the expansion of said ceramic tube, said straight strip-shaped metal l coating extending in longitudinal direction of said ceramic tube and adapted to serve as return conductor of said line section and to create a substantially distributed shunt capacitance between said coatings.

13. A line section comprising in combination a ceramictube consisting of a ceramic material the dielectric constant of which decreases with increasing temperature, said ceramic tube having an outer cylindrical face and an inner cylindrical face; a coiled strip-shaped metal coating having a mechanical rigidity which is less than that of said ceramic tube firmly fused to said outer cylindrical face of said ceramic tube so that during temperature variations its expansion is identical to the expansion of said ceramic tube, said coiled strip-shaped metal coating extending in longitudinal direction of said ceramic tube and adapted to serve as forward conductor of said line section; a straight strip-shaped metal coating having a mechanical rigidity which is also less than that of said ceramic tube and being firmly fused to said inner face of said ceramic tube so that during temperature'variations its expansion is identical to the expansion of said ceramic tube, said straight strip-shaped metal coating extending in longitudinal direction of said ceramic tube and adapted to serve as return conductor of said line section and to create a substantially distributed shunt capacitance between said coatings; and an electrical connection between one end of said coiled strip-shaped metal coating firmly fused to said outer cylindrical face of said ceramic tube and one end of said straight strip-shaped metal coating firmly fused to said inner cylindrical face of said ceramic tube.

14. A line section comprising in combination a rigid insulating tubular member having an outer cylindrical face and an inner cylindrical face; a coiled strip-shaped metal coating having a mechanical rigidity which is less than that of said rigid insulating tubular member firmly fused to said outer cylindrical face of said rigid insulating tubular member so that during temperature variations its expansion is identical to the expansion of said rigid insulating tubular member, said coiled strip-shaped metal coating extending in longitudinal direction of said rigid insulating tubular member and adapted to serve as forward conductor of said line section; a metal coating having a mechanical rigidity which is also less than that of said rigid insulating tubular member and being firmly fused to said inner face of said rigid insulating tubular member so that during temperature variations its expansion is identical to the expansion of said rigid insulating tubular member, said metal coating extending in longitudinal direction of said rigid insulating tubular member and adapted to serve as return conductor of said line section and to create a substantially distributed shunt capacitance between said coatings; and a movable metallic adjusting member arranged within said rigid insulating tubular member; and manually operable means connected to said movable metallic adjusting member for moving the same within said rigid insulating tubular member in axial direction of the same.

15. A line section comprising in combination a ceramic tube consisting of a ceramic material the dielectric constant of which decreases with increasing temperature, said ceramic tube having an outer cylindrical face and an inner cylindrical face; a coiled strip-shaped metal coating having a mechanical rigidity which is less than that of said ceramic tube firmly fused to said outer cylindrical face of said ceramic tube so that during temperature variations its expansion is identical to the expansion of said ceramic tube, said coiled strip-shaped metal coating extending in longitudinal direction of said ceramic tube and adapted to serve as forward conductor of said line section; a straight strip-shaped metal coating having a mechanical rigidity which is also less than that of said ceramic tube and being firmly fused to said inner face of said ceramic tube so that during temperature variations its expansion is identical to the expansion of said ceramic tube, said straight strip-shaped metal coating extending in longitudinal direction of said ceramic tube and adapted to serve as return conductor of said line section and to create a substantially distributed shunt capacitance between said coatings; an electrical connection between one end of said coiled strip-shaped metal coating firmly fused to said outer cylindrical face of said ceramic tube and one end of said straight strip-shaped metal coating firmly fused to said inner cylindrical face of said ceramic tube; a movable metallic adjusting member arranged within said ceramic tube; and manually operable means connected to said movable metallic adjusting member for moving the same within said ceramic tube in axial direction of the same.

- HEINZ E. KALLMANN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,563,731 Ducas Dec. 1, 1925 1,715,319 Hauck May 28, 1929 2,134,794 Muth et a1. NOV. 1, 1938 2,226,728 Le Lande et a1 Dec. 31, 1940 2,403,349 Dolberg July 2, 1946 2,413,609 Wheeler Dec. 31, 1946 2,416,683 Finch Mar. 4, 1947 2,474,988 Sargrove July 5, 1949 

